Currently, the rate at which a bicyclist is pedaling, i.e., the cycling cadence, is measured by devices that need to be mounted to the bike, like a magnet on the crank with a sensor on the frame that measures the fluctuating magnetic field when the crank passes closely.
WO2012019654A1 discloses a sensor apparatus for determining a crank cadence and a bicycle speed. The sensor apparatus comprises a housing with an accelerometer with first and second perpendicular measurement axes, capable of providing first and second signals dependent on the two measurement axes, a wireless transmitter, and a power source. The housing comprises an attachment means for attaching the housing to a wheel of the bicycle. The sensor apparatus further comprises a first means for determining the cadence from the rate at which consecutive changes of polarity occur in the first signal, or from the rate at which consecutive positive and negative extreme values occur in the first signal, and a second means for determining the speed from the rate at which consecutive maximum and minimum extreme values occur in the second signal.
EP1992389A1 discloses a data logger for a monitoring sports which includes an accelerometer, a gyro sensor to sense angular displacement, a GPS unit to sense position and velocity, a magnetometer to sense direction of movement, a heart rate monitor, and a controller programmed to manipulate the data and provide a display of the heart rate, speed, and other sport parameters. The data can be stored or transmitted to a remote computer for use by the coach. The device is useful in football codes, athletics, swimming, snow sports and cycling.
A disadvantage of a device attached to the bike for measuring cadence is that it only works on one bike. Most sports cyclists have more than one bike and would thus need to buy and attach a cadence measuring device on each bike. In addition, attaching a cadence meter to a bike is cumbersome.